The invention relates to a device for machining a workpiece, for example by welding and cutting, by means of a machining laser beam, and to a detector device for mounting on such an apparatus.
U.S. Pat. No. 5,272,312 discloses a device for machining a workpiece, for example by welding and cutting, by means of a machining laser beam, the device comprising:
(a) a laser which generates the machining laser beam; PA1 (b) a laser machining head through which a continuous channel for the machining laser beam passes; PA1 (c) a detector device having at least one sensor, to which sensor for purposes of monitoring and controlling the machining operation a bundle of rays coming from the workpiece is supplied. PA1 (a) a laser which generates the machining laser beam; PA1 (b) a laser machining head which has passing through it (i) a continuous channel for the machining laser beam, and (ii) an observation channel through which the bundle of rays coming from the workpiece passes when the device is in use,
In this device, the "secondary light" coming from the machining zone of the workpiece is used for monitoring and regulating the machining operation. "Secondary light" shall be understood to mean those light beams of different wavelength which are generated in the machined workpiece by the machining laser beam. In this connection, the secondary light is firstly UV light, which emerges from the vapour capillary produced by the machining laser beam in the workpiece. This UV radiation can be used for monitoring and regulating different welding parameters. Moreover, from the molten region of the workpiece which lags behind the vapour capillary viewed in the direction of movement of the machining head, there issues IR radiation, which can be used to monitor the quality of the welding. In particular, by means of the IR radiation, holes or pores which have been caused by material spurting out of the weld seam can be detected and documented. In the case of the apparatus described in U.S. Pat. No. 5,272,312, a sensor sensitive to UV and a sensor sensitive to IR are provided, corresponding to the different wavelength of the said rays. In the exemplary embodiment according to FIG. 4, the two sensors are combined in a common detector device. Splitting of the rays is effected corresponding to their wavelength by a mirror, which is substantially transparent to one of the two wavelengths but reflects the other wavelength.
In the case of the known welding and cutting apparatus, the detector device is a completely separate unit from the laser machining head (which is not specifically illustrated in the prior publication), and has to be housed in the constricted space between laser machining head and workpiece so that it is able to receive the secondary radiation coming from the workpiece. For reasons of geometry this is often associated with considerable problems. Sometime the detector device has to be arranged so close to the workpiece that problems with temperature arise.